Moist heating pad

ABSTRACT

An improved heating device such as a heating pad comprising a fabric base and insulated resistance wire mounted in said pad, preferably in a backward and forward sinuous pattern, at least one thermostat connected in series with the resistance wire element at both ends by means of lead wires of a low resistance metal such as copper, each thermostat being positioned intimately with a span or straight portion forming part of a sinuous loop of resistance wire, a switch connected in series with the resistance wire, and a plurality of bars of a metal such as lead mounted in the pad. In an improved embodiment the insulation on the resistance wire is formed of a plastic material able to withstand the elevated temperatures attained by the resistance wire during operation.

Unite tates i atent 11 1 1111 3,889,101 Woods June 10, 1975 [5 MOISTHEATING PAD 2,627,018 1/1953 Duren 219/527 2,633,846 4/1953 Wray 128/256[75] Inventor: Wmds, Battle Creek 3,119,926 1 /l964 M1115 et a1..219/212 Mlch- 3,423,567 l/l969 Mills 219/212 [73] Assignee: Battle CreekEquipment Company,

Battle: Creek, Mich Primary Exammer-Volodymyr Y. Mayewsky Attorney,Agent, or FirmSamuel Kurlandsky, Esq. [22] Filed: Oct. 15, 1974 [52] US.Cl. 219/527; 128/256; 128/399; 219/529; 219/530; 219/549; 219/212 [51]Int. Cl. HOSb 3/36 [58] Field of Search 128/254, 256, 399; 219/211, 212,527, 528, 529, 530, 549

[56] References Cited UNITED STATES PATENTS 774,623 11/1904 Wales219/212 1,653,901 12/1927 Haessly 1 128/256 1,754,763 4/1930 Nunnallyw.219/527 X 2,154,184 4/1939 Roberts 219/528 2,215,042 9/1940 Howard eta1, 219/529 2,393,182 l/l946 Newell 1 219/212 2,590,212 3/1952 Samuels128/254 [57] ABSTRACT An improved heating device such as a heating padcomprising a fabric base and insulated resistance wire mounted in saidpad, preferably in a backward and forward sinuous pattern, at least onethermostat connected in series with the resistance wire element at bothends by means of lead wires of a low resistance metal such as copper,each thermostat being positioned intimately with a span or straightportion forming part of a sinuous loop of resistance wire, a switchconnected in series with the resistance wire, and a plurality of bars ofa metal such as lead mounted in the pad. In an improved embodiment theinsulation on the resistance wire is formed of a plastic material ableto withstand the elevated temperatures attained by the resistance wireduring operation.

10 Claims, 6 Drawing Figures PATENTEDJUH 10 I975 SHEET 23 2/ 20 25 4 j mn I A (as b 1? a; w k/ JUQ v PATENTED JUN l 0 I975 SHEET MOIST HEATINGPAD BACKGROUND OF THE INVENTION l. Field of Invention The presentinvention relates to electrically operated heating devices, and is moreparticularly concerned with such devices having a heating elementmounted in a fabric, such as heating pads, blankets, clothing, and thelike.

2. Prior Art Heating pads disclosed in the prior art have been ofseveral general forms. In one form, commonly known as the spiralconstruction form, a strand of resistance wire, commonly covered withasbestos insulation, has one end at the center of the pad fastened inplace by sewing, and arranged in a spiral pattern, the spiral continuinguntil the pad reaches the desired size. In another form, the strand ofresistance wire is in a sinuous pattern, running back and forthcompletely across the pad, or lengthwise of the pad, until sufficientelongated runs have been placed on the pad to give it the desiredlength. In both of these forms of construction, the standard practice isto sew the resistance wire in place between two piles of canvas or thelike. This pattern interferes with uniform heating over the entire areaof the heating pad and commonly causes what is termed hot spots in thepad. Pads made according to either of these forms are relativelysatisfactory for some purposes, if used to supply low or moderate heatwhile lying flat, such as for the purpose of warming beds. However,where it is desired to supply heat to a surface or area that is notsubstantially level, these pads have not proved to be whollysatisfactory, largely due to their stiffness and rigidity with resultinginability to follow the contours of the surface to be heated. Thedifficulty involved, due to such stiffness and rigidity when the pad isin use, is normally referred to as bridging.

Heat is commonly prescribed as a means of relieving congestion, pain,soreness, or injury. In order to apply heat effectively, the heatsupplying mechanism must readily conform to the contour of the surfaceto be treated. This calls for a heating mechanism having a pliabilityand normally high temperature capability that has not been available oreven possible in somev of the prior art electric heating pads orblankets.

In US. Pat. No. 2,154,184, a heating pad is disclosed and claimed havinga structure in which the heating element is in the form of smallbackward and forward sinuous loops, several rows of loops being utilizedto provide a heating element for the entire pad. Such structure isconsiderably more flexible than those previously disclosed and provideda pad which was sufficiently flexible to conform to the contours of thevarious parts of the body. Additionally, thermostats are incorporated inthe pad and wired in series with the heating wire element. Thethermostats are placed intermediate the rows of heating element loops.Although the heating element disclosed in the above-referred-to patent,constitutes a material improvement over the prior art devices, it stillhas several drawbacks in that there is a large temperature lag betweenthe thermostat and the heating elements so that before the pad warms upsufficiently to provide suitable control by the thermostat, thetemperature of the heating pad first rises to an undesirably hightemperature. Additionally the asbestos insulation utilized forinsulating the resistance wire often becomes unraveled or torn,resulting in the danger of short circuits and electric shocks.

SUMMARY OF THE INVENTION Accordingly, it is an object of the presentinvention to produce a heating mechanism such as a pad, blanket or thelike which is pliable in all directions and is able to fit the contoursof parts of the body.

It is another object to provide a multi-section heating mechanismwherein each section is formed of a series of relatively short turns orloops of an electrical resistance wire element such as nichrome wire.

It is still a further object to provide a heating mechanism wherein thesections are so mounted in parallel that they hinge at the point whereone section is joined to the other.

It is an additional object to provide an electric heating pad which maybe rolled or doubled up in use, or in storage, and yet which will notcollapse, but will stay flat when unrolled or undoubled. It is anadditional object to provide a heating pad for therapeutic use whichwill readily conform to the shape of the body on which it is to be used.

It is a further object of the invention to provide a heating pad whichcan provide moist heat without the need to first wet the fabric of thepad.

It is a prime object of the present invention to provide a heating padhaving thermostats so arranged that they begin to operate and tomaintain a uniform temperature without an initial cycle in which thetemperature of the pad rises to a value considerably elevated over thedesired temperature.

It is another object to provide a heating pad having resistance wirewith an insulation which is strong and not subject to unraveling ortearing, and which remains undamaged at theelevated temperatures ofoperation of the pad.

It is another object to provide a heating pad of the type describedhaving thermostats which are adequately encapsulated and protected.

Still further objects and advantages of the invention will appear fromthe description and drawings.

To the accomplishment of the foregoing and related ends, the inventioncomprises a heating pad formed of a fabric and having resistance wireelement arranged having a suitable insulation covering and arranged in aplurality of rows each formed by a backward and forward sinuous loopingof the element to provide flexibility of the pad. Additionally, one ormore thermostats are connectedin series with the resistance wire elementon both sides by means of copper lead wires so that the thermostats maybe placed within the loops of the element intermediate two adjacentstrands of resistance wire or preferably directly adjacent a strand ofwire, and thereby be more sensitive to the temperature of the element,and thereby avoiding the initial high temperature rise of the elementbefore the thermostats are able to control the heating pad temperature.

BRIEF DESCRIPTION OF THE DRAWINGS In the annexed drawings:

FIG. 1 is a perspective view, partly broken away, of a heating padaccording to the invention.

FIG. 2 is a plan view, partly broken away, of the heating pad shown inFIG. 1.

FIG. 3 is a plan view illustrating the circuitry of the resistance wireand thermostats.

FIG. 4 is a fragmentary enlarged perspective view, partly broken away,of a portion of the heating pad shown in FIGS. 1-3.

FIG. 5 is a fragmentary enlarged cross-sectional view taken at the line55 of FIG. 4, looking in the direction of the arrows, and

FIG. 6 is a plan view of the electrical portion of a heating pad in amodified embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1-4, aheating pad 10 according to the invention is shown comprising anelectric line cord 11, a switch 12 in series therewith, and a plug 13for plugging into a main socket. The switch 12 is preferably of the typewhich is spring-loaded normally open. When the operator desires toutilize the heating pad, he must press on the switch button 120 in orderto close the switch. Current then flows as long as the button 12a ismaintained in depressed position. When the hand is removed, the circuitis automatically opened. This provides protection to the operator in theevent that he should fall asleep or fail to sense when the temperatureof the pad becomes too high. The heating pad further comprises outercover or bag 14 and inner cover or bag 15 of a canvas fabricconventionally known as duck. Within theouter covers is an inner supportsheet 16 also of duck material, and a plurality of strips 17 of duckmaterial affixed thereto. The strips have end flaps 17a folded over atthe ends. A plurality of strips or bars 18 of a metal such as a leadalloy are mounted on the support sheet 16 and have ends extendingthrough apertures provided in the support sheet and have bentover endportions 18a bent over the fabric strips 17. The metal strips 18 areformed of a lead alloy of such composition that it has a high absorptioncapability for water. Consequently, when the temperature of the heatingpad is elevated as a result of electricity passing through the heatingelements, moisture is driven off the lead strips and permeates the innerand outer coverings, providing moist heat to the area of the patient towhich the pad is applied.

As shown in FIG. 2, the line cord 11 enters the heating pad at a tubularline cord retainer 19. The heating element of the pad comprisesinsulated resistance wire 20 positioned in the form of a plurality ofsinuous loops 21, shown in FIG. 3. As further shown in FIGS. 2 and 3,the line cord 11 is connected to the resistance wire by a connector 22.Copper lead wires 26, 27, and 28 connect thermostats 24 and 25 in serieswith each other and in series with the resistance wire. As shown in thedrawings, the resistance wire is arranged in the form of banks of loops30, 31, 32 and 33, disposed intermediate the support sheet 16 and theduck fabric strips 17. The duck strips 17 are affixed to the supportsheet and maintained in position by the bent-over ends 18a of the leadstrips 18. As shown in FIGS. 2 and 3, the thermostats are so placed thatthey are positioned directly over one of the two wires of a loop 21, andpreferably in close proximity to one of the wires. Because of thisarrangement, the temperature of the thermostat and the temperature ofthe resistance wire remain close together, generally within about 10l5F.

Referring to FIGS. 4 and 5, an enlarged portion of the heating padsurrounding the thermostat 25 is shown. Shown in the Figures are theresistance wire lead 20 comprising resistance wire 41 formed of nichromeor any other resistance heating wire generally known in the art. Thewire 41 is covered with a plastic insulation sleeve 42 preferably formedof a material such as silicone rubber which has been found ideallysuited for withstanding the temperatures attained by the resistancewire. Additionally, the material is tough and flexible and does notbreak or become cut over extended periods of use. The thermostat 25 isshown and comprises a conventional commercial tubular thermostat havingan outer metallic jacket 44 and a conventional thermostat element 45inside. A plastic heatshrunk jacket 47 is positioned over the outerjacket 44 to protect the thermostat. Copper lead wires preferably havinga silicone rubber insulating jacket are connected to the thermostat. Thelead wires 27 and 28 are in turn connected in series with the electricalcircuit. As shown, the thermostat is placed in the pocket formed betweenthe support sheet 16 and the strip 17 which is held in place by the leadstrip ends 180. The resistance wire leads 20 are also disposed in thepocket and go down one pocket and up adjacent pockets. Consequently, thethermostat is positioned in close proximity to the heating wire line 20and is directly heated along its entire length by the resistance wire.Consequently, only a small temperature lag develops when the electricityis first turned on to the heating pad.

In the heating pad shown in FIGS. 1-5, only two thermostats areutilized. However, for some applications, and in order to meet certainrequirements of Underwriters Laboratory, a heating pad having a circuitas shown in FIG. 6 with four thermostats must be utilized. Showndiagramatically in FIG. 6 are banks of sinuous loops 51, 52, 53 and 54of resistance wire similar to that shown and discussed above having asilicone rubber insulating jacket. Connectors 55 and 56 connectthermostats 57, 58, 59 and 60 to the resistance wire in the banks ofloops 51-54 by means of insulated copper leads 61, 62, 63,64, and 66. Aline cord 67 having a normally open spring switch 68 in series connectsto the power main by means of a plug 69. The remaining structure of theheating pad is similar to that shown in FIGS. 1-5.

The heating pad of the present invention in its several embodiments hasmany advantages over those of the prior art. In the prior art padsasbestos was used as an insulation for the resistance wire and wasapplied to the wire generally by braiding. This had the advantage thatit was easy to expose the face of the wire through movement. Moreover,if the asbestos was wound too tight, the heating element had a tendencyto pop through. The asbestos-type insulated wire also posed a healthproblem since it contained asbestos fibers which are now becomingrecognized as harmful to human beings. In the present heating pad theresistance wire is covered with a silicone rubber jacket which canwithstand temperatures in excess of 500F. Moreover, the material is sotough and resilient that it can bend without fracturing, and also is notreadily cut on sharp surfaces.

The prior art pads also had a disadvantage in that they were directlyconnected in series with the resistance wire. As a result, they couldnot be mounted adjacent substantial lengths of resistance wire so thatthey could attain the temperature of the wire readily. Moreover, theactual contact of the thermostat with the heated resistance wire furthercontributed to poor tracking between the temperature of the heatingelement and the temperature of the thermostat. This tracking discrepancygenerally shows up when the heating pad is first turned on. In the priorart heating pads, because of poor heat transfer between the heatingelement and the thermostat, the temperature of the heating element risesquickly and in the old heating pads rose to a value of about 60F. abovethat of the thermostat before the thermostat could catch up. Because thepresent heating element has only a thin silicone rubber jacket, andsince the thermostat is now connected to the heating system by separatecopper leads, the thermostat can be mounted adjacent a substantiallength of wire representing the length of a loop. As a result of thisstructure and materials, the heating element temperature even on thefirst cycle does not exceed a value lO-15 above that of the thermostat.After the first cycle, the temperatures of the heating element andthermostat remain very close together, so that a uniform heatingtemperature is obtained.

It is to be understood that the invention is not to be limited to theexact details of operation or structures shown and described, as obviousmodifications and equivalents will be apparent to one skilled in theart.

I claim:

1. A moist heating pad comprising:

a. a flexible moisture permeable base sheet,

b. an electrical resistance wire heating element having an insulationsleeve mounted on said flexible base in a pattern comprising a pluralityof substantially parallel banks of backward and forward sinuous loopshaving straight portions substantially perpendicular to the longitudinaldirection of said banks,

c. at least one thermostat encased in an insulation jacket connected inseries with said heating element and connected at both of its ends byinsulated lead wires of a highly conductive metal, said thermostat beingpositioned parallel and in close proximity to a straight portion of oneloop of said heating element,

d. a plurality of strips of a water absorption lead alloy mounted onsaid flexible base sheet each within one of said sinuous loops,

e. an electrical line cord having a switch therein being electricallyconnected to said heating element, and

f. a flexible moisture permeable cover enclosing said flexible basesheet, said heating element, said metal strips and said thermostat.

2. A moist heating pad according to claim 1, wherein both the lead wiresconnected to said thermostat are of copper.

3. A moist heating pad according to claim 1, wherein said heatingelement is formed of nichrome wire.

4. A moist heating pad according to claim 1, wherein said insulationsleeve of said heater element is formed of silicone rubber.

5. A moist heating pad according to claim 1, wherein said thermostat isencased in a plastic heat-shrunk jacket.

6. A moist heating pad according to claim 5, wherein one of the leadwires connected to-said thermostat is enclosed within said heat-shrunkjacket.

7. A moist heating pad according to claim 1, wherein said flexible basesheet is formed of fabric.

8. A moist heating pad according to claim 1, having a plurality ofthermostats each similarly mounted.

9. A moist heating pad according to claim 1, having an inner coverwithin said outer cover, both of said covers being formed of fabric.

10. A moist heating pad according to claim 1, having a fabric stripcovering each bank of sinuous loops, and affixed in place by turned-overends of said metal strips.

1. A moist heating pad comprising: a. a flexible moisture permeable basesheet, b. an electrical resistance wire heating element having aninsulation sleeve mounted on said flexible base in a pattern comprisinga plurality of substantially parallel banks of backward and forwardsinuous loops having straight portions substantially perpendicular tothe longitudinal direction of said banks, c. at least one thermostatencased in an insulation jacket connected in series with said heatingelement and connected at both of its ends by insulated lead wires of ahighly conductive metal, said thermostat being positioned parallel andin close proximity to a straight portion of one loop of said heatingelement, d. a plurality of strips of a water absorption lead alloymounted on said flexible base sheet each within one of said sinuousloops, e. an electrical line cord having a switch therein beingelectrically connected to said heating element, and f. a flexiblemoisture permeable cover enclosing said flexible base sheet, saidheating element, said metal strips and said thermostat.
 2. A moistheating pad according to claim 1, wherein both the lead wires connectedto said thermostat are of copper.
 3. A moist heating pad according toclaim 1, wherein said heating element is formed of nichrome wire.
 4. Amoist heating pad according to claim 1, wherein said insulation sleeveof said heater element is formed of silicone rubber.
 5. A moist heatingpad according to claim 1, wherein said thermostat is encased in aplastic heat-shrunk jacket.
 6. A moist heating pad according to claim 5,wherein one of the lead wires connected to said thermostat is enclosedwithin said heat-shrunk jacket.
 7. A moist heating pad according toclaim 1, wherein said flexible base sheet is formed of fabric.
 8. Amoist heating pad according to claim 1, having a plurality ofthermostats each similarly mounted.
 9. A moist heating pad according toclaim 1, having an inner cover within said outer cover, both of saidcovers being formed of fabric.
 10. A moist heating pad according toclaim 1, having a fabric strip covering each bank of sinuous loops, andaffixed in place by turned-over ends of said metal strips.